Apparatus for bagging material

ABSTRACT

An apparatus ( 10 ) for bagging material into a stretchable bag having an open end, comprises a movable bag stretching structure ( 18 ) displaceable between a first position for receiving the bag and a second position for holding the bag in a stretched state, wherein said stretching structure ( 18 ) is provided with elongated corner members ( 70, 72 ) for accumulating the bag thereon, each of said elongated corner members ( 70, 72 ) being provided with a movable strap-like member ( 210 ) extending along the length of the corner members ( 70, 72 ) to facilitate loading and unloading the bag on and from the corner members ( 70, 72 ).

RELATED APPLICATIONS

This is a continuation of International Patent Application No.PCT/CA2006/002115 filed Dec. 22, 2006, which claims benefit of U.S.Provisional Application No. 60/752,913 filed Dec. 23, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for bagginggoods, such as bundles of wood, in stretchable bags.

2. Description of the Prior Art

Some wood products, such as rectangular bundles of lumber strips, needto be protected from the environment and stored in a way such as topreserve an appropriate degree of humidity and prevent UV rays fromdamaging the wood.

In the past, various bagging apparatuses have been developed to loadagricultural products into stretchable plastic tubes. However, there isstill a need for a new apparatus and method for providing effective andconvenient bagging or sheathing of rigid wood products into stretchablebags or the like.

More particularly, there is a need to more uniformly distribute thetension exerted on the film during the bagging process in order toimprove the overall quality of the bag and package and preventaccidental tearing of the bagging material. There is a need to find anew bagging process and apparatus allowing the use of thinner baggingmaterial in order to reduce the packaging costs.

SUMMARY OF THE INVENTION

It is therefore an aim of the present invention to provide an apparatusand a method for wrapping material, such as bundles, into stretchablebags.

It is also an aim of the present invention to provide such an apparatuswhich is adapted to more evenly distribute the tension in the baggingmaterial and prevent excessive stress concentration therein.

It is a further aim of the present invention to provide improvedpackaging quality at less cost.

It is still a further aim of the present invention to provide anapparatus which reduces or minimizes the stress induced into thesheathing material, thereby allowing the use of thinner film materials.

Therefore, in accordance with the present invention, there is providedan apparatus for bagging material into a stretchable bag having an openend, comprising a movable bag stretching structure displaceable betweena first position for receiving the bag and a second position for holdingthe bag in a stretched state, wherein said stretching structure isprovided with elongated corner members for accumulating the bag thereon,each corner member having a distal end with an arcuate cross-section.

In accordance with a further general aspect of the present invention,there is provided an apparatus for bagging material into a stretchablebag having an open end, comprising a movable bag stretching structuredisplaceable between a first position for receiving the bag and a secondposition for holding the bag in a stretched state, wherein saidstretching structure is provided with an elongated corner members foraccumulating the bag thereon, each corner member being provided with amovable strap-like member to facilitate loading and unloading the bag onand from the corner members.

According to a further general aspect, there is provided a method ofbagging an article into a bag comprising: a) providing a bag having anopening for receiving the article, b) loading the bag on first andsecond pairs of corner members of a stretching apparatus, the cornersmembers being displaceable along first an second orthogonal directions,c) displacing the second pair of corner members away from said firstpair of corner members along said first direction, d) displacing saidcorner members of said first pair away from one another along saidsecond direction while at the same time displacing said corner membersof said second pair in said first and second orthogonal directions awayfrom said corner members of said first pair, e) further displacing saidsecond pair of corner members away from said first pair of cornermembers along said first direction, and f) lowering the bag in a tautopen state over the article.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, showing by wayof illustration a preferred embodiment thereof, and in which:

FIG. 1 is a side elevation view of a bagging apparatus in accordancewith a preferred embodiment of the present invention;

FIG. 2 is a top plan view of the bagging apparatus of FIG. 1;

FIG. 3 is a cross-sectional view of a pair of side-by-side beltconveyors forming part of the apparatus of FIG. 1;

FIG. 4 is a schematic side elevation view of a stretching column formingpart of a stretching and bagging unit of the apparatus of FIG. 1;

FIG. 5 is a schematic front elevation view of the stretching column ofFIG. 4;

FIG. 6 is a schematic top plan view of the stretching column of FIG. 4;

FIG. 7 is a simplified front end elevation view of a pair of stretchingcolumn, one of which is equipped with a tip folding system in accordancewith one aspect of the present invention;

FIG. 8 is a simplified side elevation view of one of the stretchingcolumn and associated folding system of FIG. 7;

FIG. 9 is a schematic elevation view of a sheath lowering plate of oneof the stretching column in accordance with another embodiment of thepresent invention;

FIG. 10 is a bottom plan view of the sheath lowering plate shown in FIG.9;

FIG. 11 is a side view of a one of the stretching column having onemechanically driven strap provided on the outer corner thereof; and

FIG. 12 is a schematic representation of a preferred bag stretchingsequence.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings, and in particular to FIG. 1, a baggingapparatus 10 suited for sheathing or bagging a substantially rectangularor square bundle B of wood within a resilient sheath S will bedescribed.

The film or sheath S is provided in the form of an elongated web offlexible, stretchable, resilient plastic material that is folded in twoabout a central longitudinal axis thereof and then rolled on a mandrelor supply reel 12 with the fold line of the sheath S forming the upperedge of the roll of material (i.e. the sheath S is folded in an inverted“V” configuration on the reel 12).

The bagging apparatus 10 generally comprises a supply unit 14, a sealingand cutting unit 16 and a stretching and bagging unit 18.

The supply unit 14 comprises a loading platform 20 pivotally mounted at22 to a rectangular framework 24 supporting the sealing and cutting unit16 and the stretching and bagging unit 18 of the apparatus 10. Ahydraulic cylinder 26 extends between the framework 24 and the loadingplatform 20 to pivot the latter between a horizontal functional positionand a vertical loading position (both positions being shown in solidlines in FIG. 1). A motorized turntable 28 is mounted on the platform20. An axle 30 extends at right angles from the turntable 28 forreceiving the supply reel 12. A pivot arm 32 is pivotally mounted to aframe structure 33 mounted to the platform 20 for receiving the freedistal end of the axle 30 once the supply reel 12 has been loadedthereon. A lock pin 34 is provided to lock the pivot arm 32 to the axle30, thereby preventing axial withdrawal of the reel 12 from the axle 30.

To load a new supply reel on the axle 30, the platform 20 is firstpivoted from its horizontal position to the vertical position thereof,as indicated by arrow 35 in FIG. 1; second, the lock pin 34 is removedand the pivot arm 32 is manually pivoted away from the axle 30; andfinally, the reel 12 is slidably fitted on the axle 30. Thereafter, thepivot arm 32 is pivoted back in engagement with the axle 30 and lockedthereto, and the cylinder 26 is extended to pivot the platform 20 backto its horizontal position. A brake 36 (FIG. 2) is provided for engagingthe turntable 28 to prevent the sheath S from being unrolled from thesupply reel 12 when required or desired.

As shown in FIGS. 1 and 2, the sheath S is directed from the supply reel12 to a first pre-stretching motorized roller 38 mounted on a verticalshaft 40 which is, in turn, mounted on the loading platform 20. A secondpre-stretching motorized roller 42 (FIG. 2) is provided on the framework24 for receiving the sheath S from the first pre-stretching roller 38.The first and second pre-stretching rollers 38 and 42 cooperate topre-stretch the sheath S so as to subsequently facilitate the fullstretching thereof in the stretching and bagging unit 18. Two or moreset of pre-stretching rollers driven at increased speed from one set tothe next can be provided for pre-stretching the sheath S before the sameis transferred to the stretching and bagging unit 18.

From the second pre-stretching roller 42, the sheath S is directedbetween a pair of indexing motorized vertical rollers 44 and 46supported by the framework 24. As seen in FIG. 2, the roller 46 ismounted to a support 47. A pneumatic cylinder 45 is provided forlinearly reciprocating the support 47 and, thus, the roller 46 away fromand towards the roller 44. In use, the roller 46 is initially displacedaway from the roller 44 to an open position for receiving the sheath Sand then displaced back against the sheath S and the roller 44 to aclosed functional position for drawing the sheath S forward into theapparatus 10.

The sheath S is transferred from the indexing rollers 44 and 46 to anoverhead transport rail system 48 mounted to the framework 24. As seenin FIG. 2, the overhead transport rail system 48 includes a pair ofside-by-side axially extending belt conveyors 50 and 52 adapted toreceive therebetween the upper end of the sheath S (i.e. the end withthe fold line). The belt conveyors 50 and 52 each include an endlessflexible belt 54 extending over a pair of axially spaced-apart rollers56 and 58. The roller 58 of each pair is motorized to drive theassociated belt 54. The belt 54 of the conveyor 52 slides betweenrollers 56 and 58 on a movable plate 60 (FIG. 3) displaceable towards,and away from, the other belt conveyor 50 so as to close or open the gapdefined between the conveyors 50 and 52. A pair of pneumatic cylinders62 (FIG. 3) are provided for displacing the plate 60. When the overheadtransport system 48 is used to transport the sheath S forwardly throughthe apparatus 10, the cylinders 62 are extended and when it is desiredto release the sheath S, the cylinders 62 are retracted so as toincrease the gap between the belts 54 of the conveyors 50 and 52.

As seen in FIG. 1, the rollers 56 and 58 of the conveyors 50 and 52 aremounted on respective shafts 64. The position of the rollers 56 and 58is adjustable along the shafts 64 for allowing the apparatus 10 to beused in conjunction with sheaths of different sizes.

As shown in FIGS. 1 and 2, the sealing and cutting unit 16 is mounted tothe framework 24 between the indexing rollers 44 and the overheadtransport rail system 48. The sealing and cutting unit 16 generallycomprises a vertically displaceable cutting blade (not shown) and a pairof vertically extending elongated heating elements 66 facing each otherfrom opposite sides of the central axis of the apparatus 10. The heatingelements 66 are positioned to receive the sheath S therebetween and aredisplaceable towards, and away from, each other between a closedoperative position and an open idle position. Pneumatic cylinders, suchas those illustrated at 68 in FIG. 1, are provided for displacing theheating elements 66 between the open and closed positions thereof. Eachheating element can be provided with a pair of heating bands (not shown)to simultaneously seal the sheath S on each side of the cut. It is alsounderstood that a linear actuator (not shown) is provided for displacingthe cutting blade in upward and downward directions to effect cutting ofa desired length of sheath S.

Referring to FIGS. 1 and 2, it can be seen that the stretching/baggingunit 18 comprises an upstream pair of stretching columns 70 and anidentical pair of downstream stretching columns 72. The upstreamstretching columns 70 are slidably mounted in linear front transversalrails 74 (FIG. 1) and are displaceable towards, and away from, eachother by means of a pair of cylinders 76 (FIG. 2) mounted in anend-to-end relationship between the upstream stretching columns 70.Likewise, the downstream stretching columns 72 are slidably mounted inlinear transversal rails 78 and are displaceable towards, and away from,each other by means of a pair of cylinders 80 mounted in an end-to-endrelationship between the downstream stretching columns 72. Thetransversal rails 74 form part of a front carriage 82 mounted in linearaxially extending rails 84 provided on top of the framework 24.Similarly, the transversal rails 78 form part of a rear carriage 86mounted in linear axially extending rails 88 provided on top of theframework 24. First and second ball screws 90 and 92 are respectivelyengaged with first and second ball nuts 94 and 96 for respectivelydisplacing the front and rear carriages 82 and 86 along the longitudinalaxis of the apparatus 10, as illustrated in FIG. 1. The first and secondball screws 90 and 92 are driven by respective electric rotary motors 98and 100. Accordingly, the ball screws 90 and 92 are operable to displacethe pair of upstream stretching columns 70 and the pair of downstreamstretching columns 72 towards, and away from, each other along thelongitudinal axis of the apparatus 10.

As seen in FIGS. 4, 5 and 6, each column 70/72 comprises on opposedsides thereof a pair of lower suction members 102 for opening the sheathS after the same has been cut and sealed so as to form a bag open at itsbottom (FIG. 5). Each lower suction member 102 includes a hollowperforated planar head 104 which is connected to a pneumatic cylinder105 (FIG. 6) for allowing the same to be linearly displaced relative tothe associated column 70/72 towards and away from the sheath S. A vacuumpump (not shown) or the like is provided for drawing air into thesuction members 102 through the perforated heads 104 thereof. Eachcolumn 70/72 is further provided with an upper suction member 106 havinga perforated face plate 108 through which air can be drawn by operationof the vacuum pump. As opposed to the perforated heads 104 of the lowersuction members 102, which are located on the inner side of the columns70 and 72, the perforated face plates 108 of the upper suction members106 are located on the outer side of the columns 70 and 72 so as toretain the bag when the same has been turned inside out over the columns70 and 72, as will explained hereinbelow.

Each stretching column 70/72 is further provided on opposed lateralsides thereof with a pair of rotary gripping arms 110. As seen in FIG.5, each rotary gripping arm 110 includes an arcuate arm segment 112which is 180 degrees pivotable relative to the associated column 70/72for allowing the bag to be turned inside out over the columns 70 and 72.Each rotary gripping arm 110 is linearly displaceable in a vertical slot114 defined in the associated column 70/72. An actuator 116, such as arodless TOL-O-MATIC actuator, can be provided within each column 70/72for linearly displacing the associated pair of rotary gripping arms 110.

Each rotary gripping arm 110 is provided with a stationary grippingfinger 118 and a pivotable gripping finger 120. A pneumatic cylinder 122is provided for displacing the pivotable gripping finger 120 between anopen position and a closed position wherein the pivotable grippingfinger 120 is urged against the associated stationary finger 118 toclamp a side of the bag at the mouth thereof.

Finally, as shown in FIG. 4, each column 70/72 is provided with avertically movable sheath lowering plate 124. The sheath lowering plate124 is mounted in a pair of vertical rails 126 provided on an outer sideof the associated column 70/72. The sheath lowering plate 124 isdisplaced along the rails 126 in opposed ascending and descendingdirections by means of a ball screw 128 engaged with a ball nut 130secured to the sheath lowering plate 124. An electric motor 132 isprovided for driving the ball screw 128 and, thus, cause displacement ofthe plate 124.

It is also contemplated to equip one of the front columns 70 and one ofthe rear columns 72 with a tip folding system 150 (FIGS. 7 and 8) tofold down or press down the triangular tip 152 formed by the seams atthe upstream and downstream ends of the sheath or bag. As exemplified inconnection with the columns 70, each tip folding system 150 isoperational to place the tip 152 of the associated seam of the bagagainst the corresponding face of the bundle B to be bagged so that whenthe bag is inverted onto the bundle B, the tip 152 of the seam is foldedinto the outer surface of the bag itself, as opposed of extendingupwardly from one end of the bundle B.

Each tip folding system 150 generally includes an arcuate arm 154slidable between an extended position (shown in broken lines in FIG. 7)and a retracted position within a guiding structure 156 provided on aninner facing side of the associated column 70/72. The arm 154 isdisplaced by operation of a pneumatic cylinder 158 mounted within thecolumn 70/72. According to one embodiment of the present invention, thepneumatic cylinder 158 has a 36 inches stroke. By extending thepneumatic cylinder 158 while the bag is stretched and turned inside outover the columns 70 and 72, the arm 154 is lowered so as to place andmaintain the tip 152 of the seam against the associated end face of thebundle B, as illustrated in FIG. 7. The subsequent lowering of thevertically movable sheath lowering plate 124 will cause the bag to beinverted onto the bundle B with the tip 152 covered by or folded intothe exterior surface of the bag so as to form a pleat in the bag at eachend of the bagged bundle. After the folding operation, the pleat formedby the tip 152 can be sealed or otherwise secured in place to preventthe same from being unfolded while the bagged bundle is transported fromone location to another.

As seen in FIG. 1, the bundle B is supported in position within theframework 24 underneath the overhead transport system 48 by a rollerconveyor 134. It is understood that an entry conveyor (not shown) and anexit conveyor (not shown) are also provided at opposed ends of theapparatus 10.

In operation, a length of sheath S is drawn into the apparatus 10 fromthe supply reel 12 between the indexing rollers 44 and the overheadtransport rail system 48 above the bundle B so as to determine thelength of sheath S to be cut in accordance with the bundle length. Then,the sheath S is cut and sealed to form the closed downstream end of abag for the underlying bundle B and a closed upstream end for the nextbundle to be bagged. It is understood that the upstream end of thesheath S has been previously sealed during a previous bagging cycle.After, the sheath S has been cut and sealed, the overhead transport railsystem 48 is powered back to displace the so-formed downwardly facingopen bag directly above the underlying bundle B.

Then, the cylinders 76 and 80 are operated to displace the columns 70and 72 towards the sides of the bag and the mouth thereof is opened byextending the lower suction members 102 next to the opposed externalsides of the bag and by subsequently operating the vacuum pump to causethe lower end of the bag to be drawn against the perforated heads 104 ofthe lower suction members 102, as illustrated in FIG. 5. Once the mouthof the bag has been opened by the bottom suction members 102, the rotarygripping arms 110 are pivoted, as indicated by arrow 136 in FIG. 5, andthe gripping fingers 118 and 120 thereof become closed against the sidesof the bag. The suction at the perforated heads 104 of the lower suctionmembers 102 is then stopped and the overhead transport rail system 48 isdisplaced to an open position thereof in order to release the closedupper end of the bag.

Thereafter, the bag is turned inside out over the four columns 70 and 72by imparting a rotation of 180 degrees to the rotary gripping arms 110in the direction indicated by arrow 138 in FIG. 5. The bag is thenfitted about the columns 70 and 72 by linearly displacing the rotarygripping arms 110 to the upper end of the associated slot 114, as shownin FIG. 5. The bag is accumulated without folds in a fully expandedcondition on the columns 70 and 72. The length of the column 70 and 72is thus selected to be greater than the height of the product to bebagged and the corresponding depthwise dimensions of the bag. Air isthen drawn into the upper suction members 106 to retain the bag and thegripping fingers 118 and 120 of all the gripping arms 110 are opened torelease the bag therefrom. The open mouth of the bag is then at theupper end thereof.

Once the bag has been properly inverted and fitted about the columns 70and 72, the cylinders 76 and 80 are actuated to stretch the bag in thetransversal direction of the bundle B and the framework 24. Then, theball screws 90 and 92 are operated to stretch the bag in thelongitudinal direction of the bundle B. At this point, the vacuum pumpcan be shut down. The cylinders 158 are then extended to lower the arms150 to position the tips 152 of the seams at the downstream and upstreamends of the bag against the corresponding faces of the bundle B, asillustrated in FIG. 7. The stretching procedure could be sequential orsimultaneous, where all four columns 70, 72 move or where three columns70, 72 move and one stays fixed or where two columns 70, 72 move and twostay fixed. Sequential stretching of the bag in the transversal andlongitudinal directions is preferred in that in reduced the stressapplied on the sheath material.

FIG. 12 illustrates a preferred bag stretching sequence. The downstreamcolumns 72 are first displace in an axially downstream direction (i.e.parallel the central axis of the apparatus) away from the upstreamcolumns 70. The bag is maintained is this first stretching state forabout 1.2 seconds. Then, the upstream columns 70 are displaced laterallyoutwardly while the downstream columns 72 are simultaneously displacedat a same rate in a downstream direction and a laterally outwarddirection. The movement of the downstream columns 72 has thus a lateralor transversal component (i.e. perpendicular to the central axis of theapparatus) and a longitudinal axial component (i.e. parallel to thecentral axis of the apparatus). The distance travelled by the upstreamcolumns 70 and the downstream columns 72 in the transversal direction isequal. Finally, the downstream columns 72 are further displaced awayfrom the upstream columns 70 in a purely axially downstream direction.This stretching procedure has been found to induce less stretching marksat the corners of the bags.

The taut open end bag is then lowered onto the underlying bundle byactuating the ball screws 128 so as to downwardly displace the sheathlowering plates 124 and cause the bag to be inverted on the bundle B asthe top surface of the bundle B engages the bottom closed end of the bagopposite the open end thereof. Once, the bag has been fitted on thebundle B with the tips 152 of the seams folded inwards, the arms 154 areretracted and the plates 124 are displaced upwardly. The stretchingcolumns 70 and 72 are then returned to their initial positions.Thereafter, the bagged bundle is displaced to a storage location andanother bundle may be bagged as per the cycle described hereinabove.

FIGS. 9, 10 and show other possible embodiments of a sheath loweringplate 124′. AS shown in FIG. 9, each sheath lowering plate 124′ includesfirst and second vertical panels extending from a common corner andequipped with at least one movable strap 210 (two in the example shownin FIGS. 9 and 10 and one in the example of FIG. 11) to help the sheathto slide off itself over the sheath lowering plate 124′. Each strap 210extends longitudinally over opposed front and back faces of the sheathlowering plate 124′ and runs over pulleys, rollers 212 or other suitabledriving elements provided at opposed upper and lower ends of the sheathlowering plate 124′. The straps 210 are preferably power driven. Forinstance, a bi-directional motor (not shown) could be operativelyconnected to one of the rollers 212 engaged with the straps 210 to drivethe straps 210 in one of first and second directions. It is alsounderstood that the straps 210 could be provided in various forms,including any suitable movable endless belt or chain-like members.

In the event that only one movable strap 210 is provided by sheathlowering plate 124′ as shown in FIG. 11, the moveable strap 210 ispreferably centrally located relative to the plate 124′ (i.e. at theoutside corner thereof). If there are two moveable straps 210 then theycould be located at a certain distant, preferably but not necessarilyequidistant to the center of the plate 124′. If there are three moveablestraps then they could be located in a similar fashion to the 2-strapsystem however with a third strap in the center of the longitudinalplane or could be located in any geometry as long as it is in thelongitudinal direction. It is also understood that there could be morethan three straps per plate. Any suitable permutation is alsocontemplated.

In use, the straps 210 are first driven in a first loading direction tofacilitate the loading of the bag over the columns 70,72 after therotary arms 110 have been pivoted in the direction indicated by arrow138 in FIG. 5 in order to turn the bag inside out. The straps 210 aresubsequently driven in a second opposed direction to help the bag toslide off from the plate 124′ while the same are lowered in order toapply the sheath over the underlying bundle to be bagged.

The use of movable straps 210 or the like is advantageous in that itcontributes to minimize the stress on the sheath material and thuspermit the use of thinner sheath material or films.

The coefficient of friction (CoF) of the moveable straps 210 has aneffect on the overall quality of the bag and package. The portion of thethickness of the strap protruding from the outside surface of the plate124′ also influences the quality of the bag. For instance, a strap witha high CoF does not allow the film to move laterally on the bagstretching columns, whereas a strap with a low CoF does allow the filmto move laterally on the columns. By allowing the film (or the bag) tomove laterally, the film has the opportunity to equally distribute thetension on its full length rather than concentrate the tension in agiven area. Although the overall degree of stretching is 3-5% (measuredby taking the circumference of the un-stretched formed bag as comparedto the overall circumference of the bundle), the degree of stretching ateach corner can be as high as 30%. With this degree of stretch at thecorners, it has been found that the film exhibits stretch marks and thisbecomes the weakest point in the package, especially at the top corners(i.e. the corners with 3 faces). By allowing the tension to more evenlyand distribute itself, it has been found that there are less stretchmarks at the top corners. The use of a high slip or low CoF strap allowsthe film to adjust itself (move) and better control the stretch factor.The areas with low tension equilibrate with the high tension areas. Thisresult in material savings since a thinner film coupled with a low CoFstrap works as well as a thicker film coupled with a high CoF strap. Forinstance, a 3.5 mil film+ strap with 0.2 CoF works as well as a 4.0 milfilm+ strap with 1.0 CoF.

The CoF of the strap should be less than 0.3 and preferably about 0.1. ACoF of 0.14 has been obtained with a lubricated ropanyl EM 8/2 00+05clear AS strap.

It has also been found that the thickness of the strap and moreparticularly the distance at which protrude the straps from the outersurface of the plates 124′ of the stretching columns has an impact onthe tension distribution in the film. For instance, a 1/16 inch thickstrap provides better results than a ⅛ inch thick strap because itallows the film to move more easily and cause less tension in the film.Alternatively, a recessed strap could work as well. As a general rule,it can be said that the strap should not protrude more than ½, inch fromthe outer surface of the plate 124′ and preferably less than ⅛ inch.

As shown in FIG. 10, the lower end of each sheath lowering plate 124′has a generally widening rounded configuration. The lower end of theplate 124′ preferably generally extends along an arc of circle in ahorizontal plane (instead of the two 90 degrees side portions at theupper end portion of the generally L-shaped plate 124′). Thisadvantageously eliminates any sharp edges that could potentially damagethe sheath during the sheath transfer process. It also contributes tomore uniformly distribute the tension in the sheath during thestretching process in that it reduces the amount of stress applied tothe corners of the bag which is known to be the most solicited regionsof the bag.

Also an upwardly extending recess 214 is preferably provided in acentral region of the lower end of the plate 124′ at a locationgenerally corresponding to the fold line of the upper L-shaped endportion of the plate 124′. The upwardly extending recess defines an arcwhich has a smaller radius than the one defined by the lower edge of theplate 124′ in the horizontal plane. By so smoothing the lower cornerregion of the plate 124′, the amount of stress applied at the corner ofthe bag can be reduced, thereby providing for the use of cheaper andthinner bagging materials.

Finally, as shown in FIG. 9, idle rollers 216 mounted for free rotationon respective axles can also be provided at the lower end of each cornerplate 124′ to facilitate loading and unloading of the bag on the cornerplate 124′.

1. An apparatus for bagging material into a stretchable bag having anopen end, comprising a movable bag stretching structure displaceablebetween a first position for receiving the bag and a second position forholding the bag in a stretched state, wherein said stretching structureis provided with elongated corner members for accumulating the bagthereon, each of said elongated corner members being provided with amovable strap-like member extending along the length of the cornermembers to facilitate loading and unloading the bag on and from thecorner members.
 2. The apparatus defined in claim 1, wherein the movablestrap-like members are power driven by a bi-directional motor.
 3. Theapparatus defined in claim 1, wherein each strap-like member has acoefficient of friction (CoF) which is less or equal to 0.3.
 4. Theapparatus defined in claim 1, wherein the CoF is about 0.1.
 5. Theapparatus defined in claim 1, wherein the movable strap-like membersprotrude from an outer surface of the elongated corner members by adistance (D) of ¼ inch or less.
 6. The apparatus defined in claim 1,wherein D is equal to about ⅛ inch.
 7. The apparatus defined in claim 1,wherein each of said elongated corner members comprises a pair of sideplates extending from a corner, and wherein said movable strap-likemember extends along said corner.
 8. The apparatus defined in claim 7,wherein each of said elongated corner members has rounded lower edges.9. The apparatus defined in claim 1, where each of said elongated cornermembers has a pair of side plates extending from a corner edge, andwherein an elongated slot extends upwardly along said corner edge from alower distal end of the side plates.
 10. A method of bagging an articleinto a bag comprising: a) providing a bag having an opening forreceiving the article, b) loading the bag on first and second pairs ofcorner members of a stretching apparatus, the corners members beingdisplaceable along first an second orthogonal directions, c) displacingthe second pair of corner members away from said first pair of cornermembers along said first direction, d) displacing said corner members ofsaid first pair away from one another along said second direction whileat the same time displacing said corner members of said second pair insaid first and second orthogonal directions away from said cornermembers of said first pair, e) further displacing said second pair ofcorner members away from said first pair of corner members along saidfirst direction, and f) lowering the bag in a taut open state over thearticle.
 11. The method defined in claim 10, comprising holding the bagin a first taut open state for a predetermined period of time betweensteps c) and d).